Note: Descriptions are shown in the official language in which they were submitted.
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'M 0118 , A FEMORAL_COMPONF.NT_FOR A HIP PRO~STHESIS
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The present invention relates to a femoral component for a
hip prosthesis to be used in hip arthroplasty. It is possible
llto reduce and~or eliminate severe pain in hip joints as a
5 1i result of arthritis or other infirmities by implanting a stem
! within a femoral intramedullary canal. A ball on the proximal
¦lend of the stem cooperates with a socket of an acetabulum to
¦ provide for articulation between the femur and the aceta~ulum
jafter the femoral head has been resected and the intramedullary
Icanal has been cleared of cancellous bone proximally and fatty
~¦tissue distally. In order to maintain pain-free articulation
of the hip joint following implantation of the stem, it is
limportant that the stem be securely fastened to the
¦intramedullary canal. Such fastening can be accomplished with
a bone cement which adheres to the stem and the wall of the
intramedullary canal. In addition, numerous stems have been
provided witb a porous surface as taught by U.S. Patent
3,605,123 to either accommodate adherence with the bone cement
or enhance a press fit between the porous surface and the wall
of the intramedullary canal. If a press fit is desired with
the intramedullary canal, the stem contour should closely match
the contour of the intramedullary canal so that the porous
surface is in intimate contact with bone, thereby ensbling bone
to grow into the porous surface.
¦ In an attempt to design a femoral component for a press fit
¦attachment to the wall of an intramedullary canal, United
States Patent 4,589,883 (Kenna) teaches a proximal portion
which is elliptical in cross section with its major and minor
axes twisting along a proximal direction. Consequently, a
Il l
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sy~ trical colltour ls provided for at each cross s~ction of the
femoral component in the Kenna patent. A different approach to
matching the contour o~ the intramedullary canal is taught by
IIU.S. Patent 4,435,854 (Keller) wherein the longitudinal axis of
5 1l the femoral component is imparted with a curvature in the
anterior-posterior plane in the form of an S-shape. Although
¦these patents address the issue of a femoral component to
Iclosely fit the intramedullary canal, it is believed that the
¦anatomic structure for the intramedullary canal does not lend
litself to a symmetrical femoral component.
t
It is an object of the present invention to provide a
femoral component which more accurately reflects the anatomic
contour for the intramedullary canal.
In the present invention, a femoral component for a hip
prosthesis includes a proximal portion with an as~mmetric
contour to define an anterior side which forms an acute angle
with a lateral side and the posterior side approacSes the
anterior side in the direction of the medial side.
Furthermore, the medial side is arcuate in shape while the
other sides include linear edges in cross section.
In the drawings, Figure l is a side view of the femoral
component of the present invention as contemplated for a right
femur. Figure 2 is a left side view of Figure l. Figure 3 is
a cross sectional view taken along line 3-3 of Figure 2.
Figure 4 is a back view of Figure l. Figures 5-8 are cross
sectional views tsken along lines 5-8 of Figures l and 2.
Figure 9 is an overlay of numerous cross sectional views
similar to Figures 5-8.
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A fel~oral component lO includes a distal end 12 and a
proximal end 14. As is well known, the femoral component is
intended to fit within an intramedullary canal of a femur (not
shown) such that the proximal end extends outwardly from the
intramedullary canal of the femur to cooperate with an
acetabulum via a ball or the like carried at the proximal end
14. A distal portion 16 includes a plurality of grooves 18
extending longitudinally. A center portion 20 defines a
circular outer surface 22 as shown in Figure S such that a
straight longitudinal axis 23 intersects the center portion
20. A proximal portion 24 includes a porous surface 26
encircling the femoral component and a neck 28 adapted to carry
a ball 30 shown in phantom in Fig. 1. An aperture 31 adjacent
the neck 28 accommodates a tool for removing the femoral
component from the intramedullary canal. The porous surface 26
is designed to extend outwardly from the proximal portion
albeit a small extension of about .5mm past the adjacent smooth
surface of the proximal portion.
As shown in Figure 2, the proximal portion 24 and the
distal portion 16 bend in an anterior direction while the
center portion 20 is in alignment with the longitudinal axis
23. Figure 3 illustrates a-chamfer 32 on the anterior side to
aYoid impingement of the distal end 12 into the bone
surrounding the intramedullary canal at that location. Figures
l and 4 illustrate a compound medial curve to accommodate a
closer fit between the component 10 and an intramedullary
canal. In this regard a first portion of the compound medial
curve adjacent center portion 20 defines an arc with a radius
A. A second portion of the compound medial curve defines an
arc with a radius A, smaller than B, and a third portion of the
mpound medial curve defines an arc with 8 rsdius C smaller
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1296140
than B. The changes ln radii appear slight for c~ch of the
! three arc portions of the compound medial curve, however, these
changes are believed to more accurately fill the intramedullary
i¦canal so that the desired press fit of the femoral component
'¦within the intramedullary canal provies for contiguous
engagement of the femoral component with substantially all of
the wall of the intramedullary canal adjacent the medial curve.
Turning to Figures 6-8, the proximal portion 24 defines an
asymmetrical contour illustrated by 8 lateral side 34, a
posterior side 36, a medial side 38 and an anterior side 40.
Throughout the proximal portion 24, the medial side 38 defines
an arcuate surface with a varying radius of curvature that
generates an arcuate bulge 33 (see Figure 8) near the anterior
side at a proximal location coinciding with cross-sectional
line 8-8 in Figure l. The lateral, posterior and anterior
sides define linear edges 35, 37. and 39, respectively, in
cross section with arcuste corners 41 and 43 therebetween. The
anterior linear edge 39 cooperates with the lateral linear edge
35 to form an acute angle of about 670 while the posterior
linear edge 37 cooperates with the lateral linear edge 35 to
form a slightly obtuse angle of about 930. Consequently. the
anterior side 40 approaches the posterior side 36 from the
lateral side 34 to the medial side 38. To accommodate the
angular orientation of the lateral edge 35, the posterior edge
37 and the anterior edge 39, the arcuate corner 41 defines an
arc of curvature which is greater in length than an arc of
curvature for the corner 43.
Turning to Figure 9, a plurality of cross sectional views
taken in the same manner as Figures 6-8 are overlayed with the
~ ~ lonS dinal axis 23 indicated as a point of reference. The
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most distal cross scction is shown at 50 and the most proximal
¦I cross section is shown at 52. The posterior side 36 shows the
linear ed~es for cross sections 50 and 52 in alignment so that
I the posterior side 36 is substantially parallel with the
! longitudinal axis with only a slight curve, while the other
sides are offset as described hereinafter. The posterior side
has a curve albeit very slight so that the posterior side
approaches the longitudinal axis 23 from the center portion 20
to the proximal portion 24, see Fig. 2. The radius of the
posterior side curve is large, i.e. the change or movement of
¦the surface toward the axis is small so that the posterior side
edges appear to be coincident along the posterior face in Fig.
9. The lateral side 34 shows edges in cross section which
¦,initially extend away from the axis 23 to form a hump 45 (see
Figures 1 and 4) as you move proximally away from cross section
50. As you continue moving proximally away from hump 45, the
edges for the lateral side move toward the axis 23 in a linear
manner. Between the hump 45 and the cross section 50, the
lateral side 34 exhibits a transition from an arcuate edge as
shown at Figure 5, to a flat edge as shown at Figure 6, to a
flat angled edge as shown at Figure 7. Between the hump 45 and
the cross section 52, the lateral side 34 forms edges 35 in
cross section which are parallel and approach axis 23. The
anterior side 40 extends away from the longitudinal axis 23
from the distal cross section 50 to the proximal cross section
52. The distal cross section 50 for the medial side 38
illustrates a substantially circular arcuate edge while at the
proximal cross section 52 for the medial side 38, the arcuate
edge is distorted outwardly to form the bulge 33 near the
anter r sidc 40.
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In view of the foregoing description of femoral componerlt
10, it is seen that the outer contour of the proximal portion
24 is designed asymmetrically to substantially match fln
I''anatomic envelope of the intramedullary canal. As a result,
l,each side of the femoral component lO in the proximal portion
i 2~ includes its own distinct geometry. A femoral component
constructed in this manner is believed to closely fit the
intramedullary canal along its anatomic axis, thereby
¦generating a substantially contiguous engagement between the
Eemoral component snd the wall of the ~ntramedu11ary cans1.
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